linux-kernel - Re: [PATCH 1/4] PM / Wakeirq: Add minimal device wakeirq helper functions

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Date:	Fri, 6 Mar 2015 14:05:43 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Tony Lindgren <tony@...mide.com>
cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Andreas Fenkart <afenkart@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Felipe Balbi <balbi@...com>,
	Huiquan Zhong <huiquan.zhong@...el.com>,
	Kevin Hilman <khilman@...nel.org>, NeilBrown <neilb@...e.de>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Nishanth Menon <nm@...com>,
	Peter Hurley <peter@...leysoftware.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	<linux-kernel@...r.kernel.org>, <linux-serial@...r.kernel.org>,
	<linux-omap@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: [PATCH 1/4] PM / Wakeirq: Add minimal device wakeirq helper
 functions

On Fri, 6 Mar 2015, Tony Lindgren wrote:

> > > +	struct wakeirq_source *wirq = _wirq;
> > > +	irqreturn_t ret = IRQ_NONE;
> > > +
> > > +	/* We don't want RPM_ASYNC or RPM_NOWAIT here */
> > > +	if (pm_runtime_suspended(wirq->dev)) {
> > 
> > What if the device is resumed on a different CPU right here?
> 
> Good point, sounds like we need to do this in some pm_runtime
> function directly for the locking.
>  
> > > +		pm_runtime_mark_last_busy(wirq->dev);
> > > +		pm_runtime_resume(wirq->dev);
> > 
> > Calling this with disabled interrupts is a bad idea in general.
> > Is the device guaranteed to have power.irq_safe set?
> 
> Well right now it's using threaded irq, and I'd like to get rid of
> the pm_runtime calls in the regular driver interrupts completely.
> We need to ensure the device runtime_resume is completed before
> returning IRQ_HANDLED here.

In general, runtime_resume methods are allowed to sleep.  They can't be
used in an interrupt handler top half unless the driver has
specifically promised they are IRQ-safe.  That's what Rafael was
getting at.

Of course, if this routine is a threaded-irq bottom half then there's 
no problem.

> > I guess what you want to call here is pm_request_resume() and
> > I wouldn't say that calling pm_runtime_mark_last_busy() on a
> > suspended device was valid.
> 
> I'll verify again, but I believe the issue was that without doing
> mark_last_busy here the device falls back asleep right away.
> That probably should be fixed in pm_runtime in general if that's
> the case.

It's up to the subsystem to handle this.  For example, the USB 
subsystem's runtime-resume routine calls pm_runtime_mark_last_busy.

> Considering the above, should we add a new function something like
> pm_resume_complete() that does not need irq_safe set but does
> not return until the device has completed resume?

That doesn't make sense.  You're asking for a routine that is allowed
to sleep but can safely be called in interrupt context.

Alan Stern

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